1. Field of the Invention
The present invention relates to an apparatus for recording information in an optical information recording medium using holography, and/or for reproducing the information from the optical information recording medium.
2. Description of the Related Art
Recently, standard of Blu-ray Disc using blue-violet semiconductor laser has realized commercialization of optical disc with recording density of approximately 50 GB in the consumer market. The optical disc is highly demanded to have capacity as large as that of the HDD (Hard Disc Drive) with size ranging from 100 GB to 1 TB.
However, new type storage technology that is different from the one using short wavelength and objective lens with large NA is required for the purpose of realizing the superdense optical disc.
There has been a trend to study storage technology for next generation, and the holographic recording technology for recording digital information using holography has been focused.
The holographic recording technology is used for recording information by generating a refractive-index modulation in the recording medium using an interference pattern generated by overlapping a signal beam which contains page data information two-dimensionally modulated by a spatial light modulator and a reference beam within the recording medium.
Upon reproduction of the information, when radiating the reference beam used for recording to the recording medium in the same arrangement, the hologram serves as a diffraction grating to generate diffraction beam in accordance with the interference pattern recorded in the recording medium. The diffraction beam is recovered as the same beam as well as the recorded signal beam and the phase information.
The recovered signal beam is two-dimensionally detected at high speeds by a photodetector such as CMOS and CCD. The holographic recording technology allows the single hologram to perform simultaneous recording/reproduction of the two-dimensional information and a plurality of page data to be overwritten at the same location. It is therefore effective for recording/reproduction of the information with large capacity at high speeds.
Japanese Unexamined Patent Publication No. 2004-272268 (Patent Document 1) discloses the holographic recording technology. The document describes the angular multiplexing recording method in which signal light flux is condensed on the optical information recording medium using a lens, and simultaneously, the reference beam of parallel light flux is radiated for interference so as to record the hologram. Then multiplexing recording is performed by displaying different page data on the spatial light modulator while changing the incident angle of the reference beam to the optical recording medium.
Japanese Unexamined Patent Publication No. 2009-86248 (Patent Document 2) and the material titled “Optical Compensation of Distorted Interference Fringes Depending on Temperature in Holographic Data Storage,” ISOM 2009 Technical Digest, TH-J-05 (Non-Patent Document 1) disclose the technology for improving quality of the hologram reproduced image.